In my opinion, the weird memory leaks that the latest snapshots have had begin even before to open any world, as can be seen here.
18w50a is close to triple the memory usage than 1.13.2 !!
MC-141267
Main menu uses a lot more RAM than it should
Resolved
Won't Fix
1
The JVM was granted a limit of 3GB of memory (-Xmx3000m) and the Windows task manager is not a reliable tool to measure the memory usage of Java processes running in that VM. Unless the process runs out of memory over time, this is not a bug.